#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>

using namespace std;
int n;

int main() {
    scanf("%d",&n);
    int ans1 = 0,ans2 = 0;
    int d = 2;
    while(d <= n) {
        ans1 += n / d;
        d *= 2;
    }
    d = 5;
    while(d <= n) {
        ans2 += n / d;
        d *= 5;
    }
    printf("%d",min(ans1,ans2));
    return 0;
}